For many years, exploration and treatment of various organs or vessels has been possible using catheter-based diagnostic and treatment systems. Such catheters are introduced through a vessel leading to the cavity of the organ to be explored or treated or alternatively may be introduced directly through an incision made in the wall of the organ. In this manner, the patient avoids the trauma and extended recuperation times typically associated with open surgical procedures.
To provide effective diagnosis or therapy, it is frequently necessary to first map the zone to be treated with great precision. Such mapping may be performed, for example, when it is desired to selectively ablate current pathways within a heart to treat atrial fibrillation. Often, the mapping procedure is complicated by difficulties in locating the zone(s) to be treated due to periodic movement of the heart throughout the cardiac cycle.
Previously-known systems for mapping the interior of a vessel or organ are described, for example, in U.S. Pat. Nos. 6,546,271 and 6,226,542. The catheters described in those patents employ electromagnetic, magnetic or acoustic sensors to map the position of a distal end of the catheter in space and then construct a three-dimensional visualization of the vessel or organ interior.
One drawback of such previously known mapping systems is that they rely on manual feedback of the catheter and/or impedance measurements to determine when the catheter is properly positioned in the vessel or organ. Those systems do not measure contact forces with the vessel or organ wall or detect contact forces applied by the catheter against the organ or vessel wall that may modify the true wall location. Instead, previously known mapping methods are time-consuming, dependent upon the skill of the clinician, and cannot compensate for artifacts created by excessive contact forces.
It therefore would be desirable to provide apparatus and methods for detecting and monitoring contact forces between a mapping catheter and the wall of the organ or vessel to permit faster and more accurate mapping. It also would be desirable to provide apparatus and methods that permit the process to be automated, thereby improving registration of measured electro-physiologic values and spatial coordinates, for example, by recording such values only where the contact forces fall within a predetermined range.
Once the topography of the vessel or organ is mapped, either the same or a different catheter may be employed to effect treatment. Depending upon the specific treatment to be applied to the vessel or organ, the catheter may comprise any of a number of end effectors, such as RF ablation electrodes, a rotary cutting head, laser ablation system, injection needle or cryogenic fluid delivery system. Exemplary systems are described, for example, in U.S. Pat. Nos. 6,120,520, 6,102,926, 5,575,787, 5,409,000 and 5,423,807.
Because the effectiveness of such end effectors often depends having the end effector in contact with the tissue of the wall of the organ or vessel, many previously-known treatment systems include expandable baskets or hooks that stabilize the distal extremity of the catheter in contact with the tissue. Such arrangements, however, may be inherently imprecise due to the motion of the organ or vessel. Moreover, the previously-known systems do not provide the ability of sense the load applied to the distal extremity of the catheter by movement of the tissue wall.
For example, in the case of a cardiac ablation system, at one extreme the creation of a gap between the end effector of the treatment system and the tissue wall may render the treatment ineffective, and inadequately ablate the tissue zone. At the other extreme, if the end effector of the catheter contacts the tissue wall with excessive force, if may inadvertently puncture the tissue, resulting in cardiac tamponade.
In view of the foregoing, it would be desirable to provide a catheter-based diagnostic or treatment system that permits sensing of the load applied to the distal extremity of the catheter, including periodic loads arising from movement of the organ or tissue. It further would be desirable to have a load sensing system coupled to control operation of the end effector, so that the end effector is operated, either manually or automatically, only when the contact force is detected to fall within a predetermined range.
U.S. Pat. No. 6,695,808 proposes several solutions to measure the force vector arising from contact with the tissue surface, including mechanical, capacitive, inductive and resistive pressure sensing devices. One drawback of such devices, however, is that they are relatively complex and must be sealed to prevent blood or other liquids from disturbing the measurements. In addition, such load sensing devices may result in an increase in the insertion profile of the distal extremity of the catheter. Still further, sensors of the types described in that patent may be subject to electromagnetic interference.
One previously-known solution for dealing with potential electromagnetic interference in the medical environment is to use light-based systems rather than electrical measurement systems, such as described in U.S. Pat. No. 6,470,205 to Bosselman. That patent describes a robotic system for performing surgery comprising a series of rigid links coupled by articulated joints. A plurality of Bragg gratings are disposed at the articulated joints so that the bend angle of each joint may be determined optically, for example, by measuring the change in the wavelength of light reflected by the Bragg gratings using an interferometer. Calculation of the bend angles does not require knowledge of the characteristics of the rigid links.
International Publication No. WO 01/33165 to Bucholtz describes an alternative spatial orientation system wherein wavelength changes measured in a triad of optical fiber strain sensors are used to compute the spatial orientation of a catheter or other medical instrument. Although the publication discloses that the strain sensors may be encased within a deformable sheath, as in Bosselman, calculation of the bend angles is not described as requiring characterization of the material properties of the deformable sheath.
Accordingly, it would be desirable to provide diagnostic and treatment apparatus, such as a catheter or guide wire, that permits sensing of loads applied to a distal extremity of the apparatus, but which do not substantially increase the insertion profile of the apparatus.
It further would be desirable to provide diagnostic and treatment apparatus, such as a catheter and guide wire, that permits computation of forces applied to a distal extremity of the apparatus, and which are substantially immune to electromagnetic interference.